1. Field of the Invention
This invention relates to the drilling, completion, and production of an essentially horizontal (hereafter “horizontal”) well section into and along a subsurface, geological formation that contains heavy, viscous hydrocarbons, as disclosed in U.S. Pat. Nos. 5,289,881 and 5,607,018, both issued to Frank J. Schuh.
2. Description of the Prior Art
U.S. Pat. No. 5,289,881 discloses in its FIG. 1 a horizontally extending well bore and casing section which contains steam injection tubing (injection tubing) 32. This injection tubing is terminated at its far down stream end by a choke 22 through which all vaporous steam (steam) injected from the surface of the earth leaves the tubing and enters the well bore casing annulus 42 for injection, through casing perforations 18, into producing zone 14. Zone 14 contains the viscous hydrocarbons that are desired to be produced to and recovered at the earth's surface. U.S. Pat. No. 5,289,881 is hereby incorporated in its entirety by reference.
U.S. Pat. No. 5,607,018 discloses a related production scheme in its FIG. 9 except that steam leaves the interior of steam injection tubing 132 by way of a series of holes 133 in that tubing. Holes 133 allow steam to exit the tubing in a direction that is directly toward casing 116, i.e., a direction that is essentially perpendicular to the long axes of both the injection tubing and the casing (liner) 116. Put another way, the exiting steam from the injection tubing is pointed directly at the inner surface of the casing, and its perforations 118, for injection of that steam into the hydrocarbon bearing formation 114 to liquefy such hydrocarbons for ultimate production to and recovery at the earth's surface. It is also disclosed in this patent, column 12, that the horizontal portion of the well bore can deviate less than 90° or more than 90° from the essentially horizontal portion of the well bore. U.S. Pat. No. 5,607,018 is hereby incorporated in its entirety by reference.
For sake of clarity, the horizontal sections of the well bore, casing and injection tubing are all shown in both of the aforesaid patents to be essentially straight along their longitudinal axes. In reality, this is not always the case. In drilling the horizontal portion of a well bore, the driller uses a commercially available instrument known as a three axis accelerometer to direct the drilling of that horizontal section. The typical accuracy for this instrument ranges from ¼ to ½ degree and can cause the driller to unknowingly deviate from the desired path. If the drilling path for any of a number of well known reasons, e.g., subsurface heterogeneities, tends too far upward or downward while drilling in the formation, the driller makes adjustments either up or down to the drilling apparatus to get the drill bit back on the desired drilling path. As explained hereinafter in greater detail, these adjustments, which are made while drilling proceeds unchecked, can result in the horizontal section of the well bore having, at least in parts thereof, a sinusoidal shape along the longitudinal axis of the well bore. Any sinusoidal configuration of the well bore is, upon completion of the well, transferred to the casing and injection tubing contained in the horizontal section of that well bore.
Thus, in reality, there can be one or more low spots in the horizontal sections of the well bore, casing, and injection tubing which can be substantial. For example, it is not uncommon for a low spot to deviate from about one to about five feet lower in elevation than the adjacent high spot.
Produced fluids, as used herein, are primarily a combination of liquid water (largely condensed steam) and liquid hydrocarbons that have been mobilized by contact with the steam injected into the formation from the injection tubing by way of the casing perforations. Produced fluids can collect in the aforementioned low spots. Undesired pools of produced fluids in such low spots not only mean lost production of desired hydrocarbons to the earth's surface, but can adversely affect the hydrocarbon production operation, e.g., by impeding or otherwise altering in a deleterious way the flow of steam in the casing annulus that surrounds the injection tubing.
Accordingly, it is highly desirable to have a horizontal well bore production scheme that overcomes the ill effects of hydrocarbons collecting in casing low spots, and this invention does just that.